1. Field of the Invention
The present invention relates to a detergent composition containing an N-acylthreonine salt and a higher fatty acid salt and, optionally, another surface-active agent. The detergent composition of the present invention exhibits little irritation and is safe. The detergent composition has improved foam maintenance, foam quality and feel upon use compared with other conventional detergent compositions.
2. Discussion of the Background
Conventional detergent compositions such as shampoo, face soap, kitchen detergent, etc. contain anionic surface-active agents such as higher fatty acid salts, polyoxyethylene alkyl ether sulfates, alkyl benzenesulfonates and the like. However, although the detergents mainly comprising such anionic surface-active agents exhibit excellent detergency, the feel upon actual use such as a creaking feel during rinsing and a stretching feel after use are not so satisfactory and, in addition, there is a disadvantage in that it exhibits much irritation to the skin and causes damage to the hair.
Surface-active agents which have been used and exhibit little irritation to the skin and hair and have an excellent detergency include N-acylamino acid salts, among them, N-acylglutamates (cf. "Functional Cosmetic Products" published by CMC, page 275, 1990), N-acyl sarcosine salts, N-acyl-N-methyl-.beta.-alanine salts, N-acylmethyltaurine salts.
Other N-acylamino acid salts have also been studied and several N-acylamino acids have been synthesized from natural amino acids and synthesizable amino acids and investigated. There have been many reports on the investigations of N-acyl derivatives of natural amino acids.
It has been recently reported that the scum which is formed by N-acylglycine salts, N-acyl-.beta.-alanine salts, etc. with calcium in tap water has been found to exhibit a good feel (cf. U.S. Pat. No. 5,185,113). However, with respect to the foaming properties of the N-acylamino acid salts in this report, they are not sufficient in terms of foam maintenance, creaminess, foaming ability and they also exhibit sliminess.
There have been rare cases in which N-(long-chain acyl) threonine (which is a kind of oxyamino acids) is used in detergent compositions. Examined Japanese Patent Publication Sho-39/029444 provides a detergent composition which does not chap the skin wherein 1-50% by weight of the above-mentioned substance is added to and compounded with a synthetic detergent of a mineral oil type or an alcohol type. However, no composition which has a satisfying feel upon use such as foam quality and finish after washing has been obtained. In the Japanese Laid-Open Patent Publication Sho-55/090594, there is a disclosure on a detergent composition containing N-acylated mixed amino acid salts and there is a description that the N-acyloxy amino acid salts exhibit a protective action to the skin and hair. However, although the resulting detergent composition is excellent in terms of the foaming and the creaking feel during rinsing, it has insufficient foam quality and finish after washing. Further, when the acylthreonine salt is used solely, there are similar problems as above and, moreover, there is another problem in that it cannot maintain a good foam.